Fasteners such as nails, staples, and truss plates are utilized extensively in the construction and assembly of countless articles from buildings to fences. The useful life of a fastener is critical to its suitability for a particular purpose. For example, a nail which is not corrosion-resistant is not suited for service where it will be exposed to outdoor weather conditions.
Coatings for fasteners have been developed to protect metal fasteners from adverse conditions. A suitable fastener coating must adequately adhere to the fastener. Typically, fasteners are made of carbon steel. Fasteners can also be made of aluminum or copper alloys such as bronze. A fastener may be zinc coated or chromate coated before a protective outer coating is applied. A suitable coating should therefore adhere to a variety of metals or metallic surfaces.
Coatings for fasteners impart desirable properties to the fasteners. For example, most protective coatings on metal fasteners provide corrosion resistance, but some coatings enable a fastener to be inserted with less force yet increase the force required to remove the fastener. A fastener coating with both above-described properties is disclosed in Lat et al., U.S. Pat. No. 4,964,774. The coating disclosed in the Lat et al. patent comprises a film forming, thermoplastic, predominantly aliphatic polyurethane resin, which is applied onto the fastener in an aqueous medium and then dried thereon.
In Campbell, Jr., U.S. Pat. No. 2,329,456, a metal coating composition comprising a copolymer of a vinyl halide, a vinyl ester of a lower saturated fatty acid and an aliphatic .alpha., .beta.-mono-olefinic carboxylic acid that exhibits improved adhesion to smooth metal surfaces is disclosed. The adhesion of the coating composition is improved by co-polymerizing the vinyl halide and the aliphatic vinyl ester with small quantities of an unsaturated carboxylic acid.
In Parkison, U.S. Pat. No. 3,853,606, a metal fastener coating that adheres to wood is disclosed. The coating comprises about 50 to about 80 percent by weight resin solids of a rosin-like resin, which is dispersed in about 20 to 50 percent by weight of an ethylene copolymer or terpolymer containing carboxyl or esterified carboxyl groups.
Even if coated, metal fasteners frequently do not satisfactorily anchor in porous materials such as plaster due to the chemical and physical properties of porous materials. Generally, the binder polymer in the plaster must be compatible, chemically, to the fastener overcoat for good adhesion to develop on drying.
Frequently, plaster-like materials such as spackling compound are applied as a finish over sheets of plasterboard which have been fastened to building frames. If the fastener used does not exhibit some sort of affinity for the spackling compound, the spackling compound will not adhere to those portions of the fastener not embedded in the plasterboard. If the spackling compound does not adhere to the exposed portions of the fastener, the finish coating will be uneven or pocked, which is unacceptable.
Therefore, a metal fastener coating which exhibits some affinity or attraction to plaster or plaster-like materials would be highly desirable.